Though the secreted Ly6/urokinase type plasminogen activator receptor (uPAR) related protein-1 (Slurp1) is one of the most abundantly expressed proteins in the cornea and is secreted into the tear film, its biological function in the ocular surface is unknown. In this project, we test the central hypothesis that Slurp1 is a key immunomodulatory molecule that suppresses inflammation at the ocular surface and is downregulated in pro-inflammatory conditions. This hypothesis is supported by our exciting preliminary data demonstrating that Slurp1 expression is (i) increased upon mouse eyelid opening when the cornea is first exposed to the environment, (ii) abrogated within 24h of bacterial lipopolysaccharide (LPS) injection or Herpes Simplex Virus type-1 (HSV-1) infection concurrent with neutrophil infiltration, (iii) decreased in the inflamed Klf4-conditional null (Klf4CN) corneas, and (iv) suppressed by pro-inflammatory interleukins IL-4 and IL-13. More importantly, (a) over-expression of Slurp1 hindered the neutrophil influx in adenoviral keratitis and (b) Slurp1 bound the uPAR ligand uPA, suggesting that Slurp1 inhibits inflammation by competitive binding of UPAR ligands. We will test our hypothesis by pursuing three Specific Aims. In Aim 1, we will establish the corneal function of Slurp1. We will determine whether reduced expression of Slurp1 is a common theme in corneal inflammation by monitoring its expression in several different experimental models. By utilizing molecular approaches to decrease or increase mouse corneal expression of Slurp1, we will determine whether these changes augment or mitigate inflammation respectively. In Aim 2, we will examine the molecular mechanisms underlying Slurp1 functions. We will determine whether Slurp1 competes with uPAR for binding to its ligands uPA, vitronectin, and integrins, resulting in decreased neutrophil migration. In Aim 3, we will interrogate the molecular events governing regulation of Slurp1 expression in healthy and inflamed corneas. We will determine if Kruppel-like transcription factor-4 (Klf4) governs the increased expression of Slurp1 upon eyelid opening, and reactive oxygen species produced in response to different stimuli suppress Slurp1 in pro-inflammatory conditions. This project, based on the novel idea that Slurp1 is a molecular switch that suppresses chronic inflammation when present in normal levels and is downregulated in pro-inflammatory conditions will generate valuable new information related to ocular surface health and disease. It makes innovative use of our unique mouse models to expand knowledge of the interface between gene regulation and innate immune response and establishes a new paradigm explaining regulation of inflammation at the ocular surface. The anticipated outcomes will define a novel target for therapeutic intervention in managing inflammatory disorders of the ocular surface.